Isolation of a strictly anaerobic strain of Staphylococcus epidermidis

Staphylococcus epidermidis is a well-characterized, nonfastidious, aerobic gram-positive coccus commonly isolated in the clinical microbiology laboratory. Although coagulase-negative staphylococci, including Staphylococcus epidermidis, are often considered a contaminant in the clinical laboratory, an increasing number of reports describe their pathogenesis, in particular in infections of prosthetic devices. This article describes the isolation of a strictly anaerobic strain of Staphylococcus epidermidis in pure culture from the site of an infected prosthetic hip. This isolate was unique in that it grew only under strictly anaerobic conditions. Initially, the isolate was thought to be a known anaerobic gram-positive coccus. However, certain key biochemical and antimicrobial tests performed as part of the standard laboratory identification procedure were not consistent with results expected for any known anaerobic gram-positive coccus; the isolate was catalase positive and metronidazole and penicillin resistant. This isolate was characterized by further biochemical analysis, antimicrobial testing, and nucleic acid sequencing. This paper presents the first documented isolation of a strictly anaerobic Staphylococcus epidermidis strain, confirmed by rpoB gene sequencing.